Dual chamber ionization smoke detector

ABSTRACT

An improved chamber assembly for a dual chamber ionization smoke detector. A fluorocarbon plastic insulation member provides a non wettable insulating dividing wall between the two chambers.

United States Patent Larsen et a1.

[ Aug. 27, 1974 DUAL CHAMBER IONIZATION SMOKE DETECTOR Inventors: LarryD. Larsen, Palatine; Joseph C.

Pekarek, Mt. Prospect, both of 111.; Arlon D. Kompelien, Richfield;Gerald D. Rork, Bloomington, both of Minn.

Assignee: Honeywell Inc., Minneapolis, Minn.

Filed: June 22, 1973 Appl. No.: 372,552

U.S. C1. 250/381, 313/54 Int. Cl. G01f 1/18 Field of Search 250/381;313/54;

[56] References Cited UNITED STATES PATENTS 3,582,646 6/1971 Ponsar313/54 X 3,710,] 10 1/1973 Lampart et a1. 250/381 3,725,011 4/1973Primary Examiner-Archie R. Borchelt Attorney, Agent, or FirmOmund R.Dahle [57] ABSTRACT An improved chamber assembly for a dual chamberionization smoke detector. A'fluorocarbon plastic insulation memberprovides a non wettable insulating dividing wall between the twochambers.

9 Clairm, 7 Drawing Figures Purt et a1 250/381 X DUAL CHAMBER IONIZATIONSMOKE DETECTOR SUMMARY OF THE INVENTION An improved chamber assembly foran ionization smoke detector which has dual chambers separated by afluorocarbon plastic divider which non wettable insulating divider hasembedded therein conductive mounting means for an electrode of each ofthe chambers and to provide a signal output terminal.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a cross-section of apreferred embodiment of the dual chamber assembly,

FIGS. 2 through 6 are drawings of various internal parts of thestructure of FIG. 1, and

FIG. 7 is an electrical block diagram of the chamber assembly in acircuit.

DESCRIPTION Referring now to FIG. 1 there is generally disclosed a dualchamber assembly for an ionization smoke detector. The upper ionizationchamber 11 is a reference chamber which is substantially or nearlysealed and does not freely admit the surrounding air. The lowerionization chamber 12 is the sensing chamber which is designed to freelyallow through it circulation of the surrounding air so that when smokeis present in the air it can be rapidly detected. A cup-like electrode13 defines the reference chamber. A flange 14 extending around theperimeter of the cup electrode 13 serves as a mounting means.

An ionizing source 15 of radioactive material enclosed in a rivet-likecontainer is fastened in the upper surface or section 16 of theelectrode I3. The section 16 has a dimple or recess 17 stamped into thesurface so that the radioactive source 15, which is mounted in therecess, does not extend out into the chamber but instead the radiationsurface of the radioactive source is substantially flush with thegeneral internal contour of the electrode 13 at the surface 16.

The sensing chamber 12 is defined by a circular cuplike electrode 13'which is identical to the previously described electrode 13 except thatan additional stamping step opens a plurality of louvers 20 to allow thefree exchange of the surrounding air into the sensing chamber.

The dual chamber assembly is mounted to a circuit board 21 which has acircular cutout to accomodate the ionization chambers. The reference andsensing chamber are separated by a fluorocarbon plastic (such asfluorinated ethylene-propylene (PE?) or polytetrafluoroethylene (TFE);by DuPont named Teflon) disc or wafer 22 shown in FIGS. 1 and 2 whichforms a non wettable insulating common wall of each chamber. Embedded inthe center of wafer 22 is a metallic insert, i.e., an electricallyconductive electrode support 23, the details of which are more clearlyseen in FIGS. 3 and 4. The conductive insert 23 includes a disc portion24 and an extension or tail portion 25 extending through the wafer to aconnection point 25' at the edge. The disc portion 24 has an offsetsection 26 to be described further below.

The second electrode of the reference chamber 11' is a metal disc 27 andit together with an identical part 2.7" in sensing chamber 12 are bothfastened to the offset section 26 of the insert 23. The details of theelectrodes 27, 27' are shown in FIGS. 5 and 6 and it will be apparentfrom FIG. 6 that these electrodes have an offset center portion 28 toprovide for the proper mounting of the electrodes.

The fluorocarbon material is used because of the high impedance circuitof electrodes 27 and 27 and the electrode support means 23. The nonwetting nature of the surface of wafer 22 ensures that there will be notendency for a film of moisture to form on the surface of the wafer toreduce the effective electrical insulation capabilities of wafer 22.

It is desired that the chamber dimension from electrode section 16 toelectrode 27 be the same as the dimension from electrode section 16' toelectrode 27'. In order to compensate for the thickness of the PC board21 in the assembly, which would otherwise unbalance the dimensionalsymmetry of the two chambers, the insert conductor 23 has a sufficientoffset in the center mounting portion 26 to achieve dimensionalsymmetry. This offset raises electrode 27' above the surface of wafer22. The electrodes 27 and 27' and the conductive mounting means 23 beingstaked together are all electrically common to each other and theterminal 25 provides for connection of the signal potential at theseelectrodes to the high impedance signal input terminal of a suitableelectrical measuring circuit 30 shown substantially in FIG. 7.

The embodiments of the invention in which an exclusive property or rightis claimed are defined as follows:

1. In an ionization smoke detector of the type having a referencechamber and a smoke sensing chamber, an improved chamber assemblycomrpising in combination:

A first cup like electrode for defining a substantially sealed referencechamber;

an inverted cup like electrode like said first electrode but also havinglouvers for admitting air to be sensed, for defining a sensing chamber;

means causing ionization within each chamber;

a fluorocarbon plastic member of wafer like shape providing a nonwettable insulating divider between said first and inverted electrodesand providing a common wall of said reference chamber and sensingchamber;

an electrically conductive electrode support embedded into said waferlike member, said support having an extension extending through saidwafer like member to a connection point at the edge thereof;

third and fourth electrodes mounted one on either side of said waferlike member to said electrode support, whereby said electrodes,electrode support and connection point are electrically common;

and fastening means for affixing together said first electrode, saidfluorocarbon plastic member with its electrodes, and said invertedelectrode.

2. The invention according to claim 1 in which said third and fourthelectrodes are disc shaped electrodes mountedcoaxially one on eitherside of said wafer like member.

3. The invention according to claim 1 in which said fluorocarbon plasticmember is fluorinated ethylene propylene (FEP).

4. The invention according to claim 1 in which said fluorocarbon plasticmember is polytetraflusaid fluorocarbon plastic member, said printedcircuit board having a cutout area within the sensing chamber.

8. The invention according to claim 7 in which said third and fourthelectrodes are dimensionally alike and in which said first and invertedelectrodes are dimensionally alike except for the louvers of saidinverted electrode. 7

9. The invention according to claim 8 in which said electrode supporthas an offset at the mounting point of said third and fourth electrodesto account for the thickness of said printed circuit board in saidassembly and provide equal inter electrode spacing in said two chambers,

1. In an ionization smoke detector of the type having a referencechamber and a smoke sensing chamber, an improved chamber assemblycomrpising in combination: A first cup like electrode for defining asubstantially sealed reference chamber; an inverted cup like electrodelike said first electrode but also having louvers for admitting air tobe sensed, for defining a sensing chamber; means causing ionizationwithin each chamber; a fluorocarbon plastic member of wafer like shapeproviding a non wettable insulating divider between said first andinverted electrodes and providing a common wall of said referencechamber and sensing chamber; an electrically conductive electrodesupport embedded into said wafer like member, said support having anextension extending through said wafer like member to a connection pointat the edge thereof; third and fourth electrodes mounted one on eitherside of said wafer like member to said electrode support, whereby saidelectrodes, electrode support and connection point are electricallycommon; and fastening means for affixing together said first electrode,said fluorocarbon plastic member with its electrodes, and said invertedelectrode.
 2. The invention according to claim 1 in which said third andfourth electrodes are disc shaped electrodes mounted coaxially one oneither side of said wafer like member.
 3. The invention according toclaim 1 in which said fluorocarbon plastic member is fluorinatedethylene propylene (FEP).
 4. The invention according to claim 1 in whichsaid fluorocarbon plastic member is polytetrafluoroethylene (TFE). 5.The invention according to claim 2 in which said fastening means affixestogether in coaxial alignment said first electrode, said fluorocarbonplastic member with its disc shaped electrodes and said invertedelectrode.
 6. The invention according to claim 1 in which said meanscausing ionization comprises a radioactive source affixed within eachchamber.
 7. The invention according to claim 1 in which the chamberassembly is mounted on a printed circuit board, the chamber assemblyfurther comprising: a printed circuit board positioned between theperimeter region of said inverted cup like electrode and saidfluorocarbon plastic member, said printed circuit board having a cutoutarea within the sensing chamber.
 8. The invention according to claim 7in which said third and fourth electrodes are dimensionally alike and inwhich said first and inverted electrodes are dimensionally alike exceptfor the louvers of said inverted electrode.
 9. The invention accordingtO claim 8 in which said electrode support has an offset at the mountingpoint of said third and fourth electrodes to account for the thicknessof said printed circuit board in said assembly and provide equal interelectrode spacing in said two chambers.